Lithium extraction from high-Mg brines using N523/esters systems

Amide extractants for lithium extraction from high-magnesium brines have demonstrated satisfactory stability and extraction efficacy. However, the presence of interfacial substance when N,N-bis(2-ethylhexyl)-acetamide (N523) is employed in isolation presents a challenge to the process operation. In this study, inexpensive modifier esters (dioctyl phthalate, DOP and acetyl tributyl citrate, ATBC) were introduced into the N523 extraction system, resolving the issue of no cascade effect with N523 alone. The effects of a range of variables on the extraction and phase separation processes were evaluated comparatively for two petroleum-based and green commercial esters. The factors included organic phase composition (including the volume ratio of extractant N523 to ester and concentration in the organic phase), coexisting ions in aqueous solution (including H+, Li+ and Cl- concentrations and Fe/Li molar ratios), and phase ratio. The complexation mechanism was characterized using the slope method and FT-IR spectrum. The results of the study demonstrated that the concentration of the total cation (Li++2Mg(2+)+H+) in the organic phase exhibited a more consistent and similar trend to that of FeCl4-. It was found that the anticipated Li+ extraction efficiency could be attained by ensuring the N523/Li molar ratio was no <11.5. Due to the fact that N523 complexes with metal ions, DOP and ATBC exhibited comparable performance and played the same role in promoting phase separation. The three-countercurrent extraction method achieved a Li+ extraction efficiency of 99.3 % and a Li/Mg separation factor of 2.8x105, with an enhanced phase-separation effect. The economical DOP and ATBC optimized the N523 system and improved the stable operation of the extraction system while reducing the cost. This provided new ideas and perspectives for its industrial application.